{	Problem: http://codeforces.ru/problemset/problem/40/B
	Verdict: Accepted
}
uses math;
var n,m,x,i,j,r:longint;
begin
read(n,m);
read(x);
r:=0;
for i:=1 to n do
  for j:=1 to m do
    if (min(min(i,j),min(n-i+1,m-j+1))=x) and (not odd(i+j)) then inc(r);
write(r);
end.
